The present invention relates to an optical scanning device for an imaging device such as a laser beam printer, and more particularly, to an optical scanning device having a controller for outputting control data, and a driver for driving a light source in accordance with the control data.
Conventionally, optical scanning devices have been employed in electrophotographic imaging devices.
As an example of the electrophotographic imaging devices, a laser beam printer is known, which employs an optical scanning device and forms an image, based on image data, on a recording sheet in accordance with an electrophotographic image forming process.
The optical scanning device for the laser beam printer is provided with a light source for emitting a beam; a deflector for deflecting the beam emitted by the light source to scan within a predetermined angular range; and an f.theta. lens which makes a spot formed, by the scanning beam, on a surface to be scanned to move at a predetermined speed. Generally, the light source includes a laser diode, and a collimator lens which converts a divergent light emitted by the laser diode to a parallel light beam.
When the optical scanning device as described above is employed in the laser beam printer, a laser beam, which is emitted by the laser diode and collimated by a collimating lens, forms a beam spot on a photoconductive drum, via the deflector such as a polygonal mirror and the f.theta. lens. The surface of the photoconductive drum is evenly charged, and the beam spot moves on the photoconductive drum in a direction parallel to a rotation axis thereof. While the spot moves on the photoconductive drum, the laser diode is driven, by a driver, so that the intensity of the emitted beam is varied (i.e., modulated) in accordance with imaging data. Further, the photoconductive drum is rotated about the rotation axis. The direction parallel to the rotational axis of the photoconductive drum is generally referred to as a main scanning direction, and the direction in which the photoconductive drum is rotated is referred to as an auxiliary scanning direction. Since the beam spot moves within a circumferential surface of the photoconductive drum as being modulated in accordance with the imaging data, a two-dimensional latent image is formed on the circumferential surface of the photoconductive drum.
The latent image is developed by adhering toner to form a toner image. Then, the toner image is transferred on a recording medium such as a recording sheet. The transferred toner image is then fused/pressed, and thereby fixed on the recording sheet.
In order to maintain tone density of the toner image on the photoconductive drum regardless of changes of ambient temperature, the intensity of the beam emitted by the laser diode should be controlled. Further, in order to control the gradation of the toner image, a period during which the laser diode is driven and/or the intensity of the emitted beam should also be controlled.
Generally, the intensity of the beam and modulation is controlled by a driver which is constituted as a single board, and control data used for controlling the power and modulation of the beam is generated and transmitted to the driver by a controller which is constituted as another single board. The controller board and the driver board are provided in the optical scanning device, separately and connected by a harness and including a plurality of data busses.
FIG. 1 shows a control system of a conventional optical scanning device including a controller 20A and a driver 10A. The controller 20A includes a control circuit 21, a power control data outputting circuit 22, and a modulation data outputting circuit 23.
To the control circuit 21, data representing temperature detected by a temperature sensor and imaging data representing an image to be drawn (printed) are input. The power control data outputting circuit 22, which is controlled by the control circuit 21, outputs power control data, as digital data, for changing the output power of a laser diode 2 so that a tone density of the toner image is adjusted. The modulation data outputting circuit 23, which is also controlled by the control circuit 21, outputs modulation data, as digital data, for modulating the beam emitted by the laser diode 2 based on the imaging data. In this example, the modulation data includes PWM (Pulse Width Modulation) data for controlling the width of the driving pulse of the laser diode.
The driver 10A has a power control signal outputting circuit 12 which is a D/A (digital to analog) circuit, a drive circuit 11, and a PWM signal outputting circuit 13.
The power control signal outputting circuit 12 receives the power control data which is transmitted from the power control data outputting circuit 22, through an eight-bit data bus 32, and outputs a power control signal to the drive circuit 11. The PWM signal outputting circuit 13 receives the PWM data transmitted from the PWM data outputting circuit 23 through an eight-bit data bus 33, and outputs a PWM signal to the drive circuit 11.
Further to the above an enabling signal is transmitted from the control circuit 21 to the drive circuit 11, through a control signal line 41. The drive circuit 11 controls the intensity of the emitted beam of the laser diode based on the power control signal, and modulates the emitted beam based on the PWM signal and the enabling signal.
In the conventional control system described above, in order to transmit the power control data and the PWM data, the controller 20A and the driver 10A are connected by eight-bit busses 32 and 33. This structure requires a relatively large interface unit at each of the controller 20A and the driver 10A since the number of connector pins and lines are relatively large, and further a relatively large room to accommodate such an interface unit is also necessary. Furthermore, if an imaging device is of a multi-beam type imaging device using a plurality of beams simultaneously, corresponding number of interface units should be provided in the optical scanning device, which increases the size of the device as well as a manufacturing cost.